This project has as its general aim the study of events important in both embryonic development and in the growth and spread of cancer cells, using as a model system embryonal carcinoma cells derived from teratocarcinomas. We have developed specialized embryonal carcinoma lines which may be grown in vitro in which several aspects of embryogenesis and carcinogenesis may be studied. In one instance, several embryonal carcinoma lines have been isolated which differ in their pattern of migration and growth, or metastasis, upon intraperitoneal injection into the mouse. One line is special in its ability to form growths in the spleen. Another teratoma line, derived from an LT ovarian teratoma, selectively seeds the ovary. An in vitro assay has been developed which correlates this in vivo behavior with the preferential attachment of the tumor cells to organ monolayer cells. These initial studies will be examined to determine if the in vitro correlation is in fact significant to the in vivo pattern. Teratoma lines from a variety of sources have been developed to study the problem of X chromosome regulation. Mutation rates of X chromosomal genes will be studied to determine the number of alleles active in these cells. Factors regulating the repression and possible re-expression of X chromosomes will be studied.